![](http://datasheet.mmic.net.cn/230000/LM20CIM7_datasheet_15592801/LM20CIM7_6.png)
2.0 Mounting
(Continued)
3.0 Capacitive Loads
The LM20 handles capacitive loading well. Without any pre-
cautions, the LM20 can drive any capacitive load less than
300 pF as shown in Figure 4 Over the specified temperature
range the LM20 has a maximum output impedance of 160
.
In an extremely noisy environment it may be necessary to
add some filtering to minimize noise pickup. It is recom-
mended that 0.1 μF be added from V
+
to GND to bypass the
power supply voltage, as shown in Figure 5 In a noisy envi-
ronment it may even be necessary to add a capacitor from
the output to ground with a series resistor as shown in Figure
5 A 1 μF output capacitor with the 160
maximum output
impedance and a 200
series resistor will form a 442 Hz
lowpass filter. Since the thermal time constant of the LM20 is
much slower, the overall response time of the LM20 will not
be significantly affected.
4.0 LM20 micro SMD Light Sensitivity
Exposing the LM20 micro SMD package to bright sunlight
may cause the output reading of the LM20 to drop by 1.5V. In
a normal office environment of fluorescent lighting the output
voltage is minimally affected (less than a millivolt drop). In ei-
ther case it is recommended that the LM20 micro SMD be
placed inside an enclosure of some type that minimizes its
light exposure. Most chassis provide more than ample pro-
tection. The LM20 does not sustain permanent damage from
light exposure. Removing the light source will cause LM20’s
output voltage to recover to the proper value.
SC70-5
no heat sink
θ
JA
(C/W)
412
312
SC70-5
small heat sink
θ
JA
(C/W)
350
266
T
J
T
A
(C)
0.2
0.17
T
J
T
A
(C)
0.19
0.15
Still air
Moving
air
See Figure 1 for PCB layout samples.
micro SMD
no heat sink
θ
JA
(C/W)
TBD
TBD
micro SMD
small heat fin
θ
JA
(C/W)
TBD
TBD
T
J
T
A
(C)
TBD
TBD
T
J
T
A
(C)
TBD
TBD
Still air
Moving
air
FIGURE 3. Temperature Rise of LM20 Due to
Self-Heating and Thermal Resistance (
θ
JA
)
DS100908-15
FIGURE 4. LM20 No Decoupling Required for
Capacitive Loads Less than 300 pF.
R (
)
200
470
680
1 k
C (μF)
1
0.1
0.01
0.001
DS100908-16
DS100908-33
FIGURE 5. LM20 with Filter for Noisy Environment and Capacitive Loading greater than 300 pF. Either placement of
resistor as shown above is just as effective.
L
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